This invention relates to a semiconductor laser capable of emitting, for example, blue to green light.
In recent years, there is a demand for semiconductor lasers capable of emitting light with short wavelengths for improving recording densities of optical disks or resolutions of laser printers, and vigorous studies have been made for realization of such lasers.
II-VI compound semiconductors are hopeful as materials to be used for fabricating such semiconductor lasers capable of emitting light with short wavelengths. In particular, ZnMgSSe compound semiconductors, which are quaternary II-VI compound semiconductors, are recognized to be suitable as materials of cladding layers and optical waveguide layers required to make on a GaAs substrate a semiconductor laser for emitting blue to green light in the band of wavelengths of 400 nm-500 nm (see, for example, Electron. Lett. 28 (1992) 1798).
As to semiconductor lasers using II-VI compound semiconductors, active studies have been made to realize oscillation at the room temperature. As a result, the present Applicant has succeeded in pulse oscillation at the room temperature by a semiconductor laser using ZnMgSSe compound semiconductors referred to above.
As to continuous oscillation at the room temperature, however, there has been no report either with a semiconductor laser using ZnMgSSe compound semiconductors mentioned above or with a semiconductor laser using II-VI compound semiconductors other than ZnMgSSe compound semiconductors.
It is therefore an object of the invention to provide a semiconductor laser using a II-VI compound semiconductor as the material of cladding layers and having the capability of continuous oscillation at high temperatures including the room temperature.
According to an aspect of the invention, there is provided a semiconductor laser comprising: a first cladding layer of a first conduction type; an active layer stacked on the first cladding layer; and a second cladding layer of a second conduction type stacked on the active layer, wherein:
the first cladding layer, the active layer and the second cladding layer are made of II-VI compound semiconductors, and
pulse oscillation occurs with characteristics of a threshold current Ith(A), a threshold voltage Vth(V) of the diode composed of the first cladding layer, the active layer and the second cladding layer, a differential resistance RS(xcexa9) of the diode after the rising, a thermal resistance Rt(K/W) and a characteristic temperature To(K), and wherein:
when two amounts xcex1 and xcex2 are defined by:
xcex1xe2x89xa1(Rt/To)IthVth 
xcex2xe2x89xa1(Rt/To)RSIth2
the point (xcex1,xcex2) exists in an area on the xcex1-xcex2 plane surrounded by the straight line xcex1=0, the straight line xcex2=0, and the curve (2ln txe2x88x921)/t, (1xe2x88x92ln t)/t2) having t as a parameter.
According to another aspect of the invention, the semiconductor laser includes a first optical waveguide layer between the first cladding layer and the active layer and includes a second optical waveguide layer between the second cladding layer and the active layer, the first optical waveguide layer and the second optical waveguide layer being made of II-IV compound semiconductors.
According to still another aspect of the invention, II-VI compound semiconductors making the first cladding layer and the second cladding layer are a ZnMgSSe compound semiconductor.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.